I like the idea of multi-tiled gates. My main passages are always wider than 2 tiles.
Actually I think the zone implementation is more logic, guards don't NEED anything to just pace back and forth and yell 'halt who goes there!' to everyone and then inspect them (or fight them). The zone could be called an inspection zone perhaps, it designates an area in which the guards will patrol (by automatic perimeter walking) and all your dwarfs will stop upon entering the zone for an inspection by the guard who will go to quickly inspect everyone entering as they enter the zone. Hostiles will of course not stop and be immediately attacked by the guards. The zone would hold the desired settings for who can pass.
OK so far.
When their are no guards present naturally everyone passes through without being checked.
An this totally negates all it's benefits. What if a dwarf sneaks out when a guard is not around, but then a guard won't let him go back, right? The reason why I suggest a gate, because it's rational to make it closed when undwarved.
What do u want to check in dwarves? It's not like there are drugs or contraband in teh game. There is not a single thing to "check" about them. Only let them pass, or not. For that reason, if I'm not mistaken, castles always had gates, not some kind of zones. And IRL if there's a place with restricted access, like subway, or a cinema, or your work or study place, everywhere, u always get your pass checked at some kind of gate (not necessary a giant door). And they are usually meant so that you can't pass when no one's looking. (except for temporary or unimportant ones)
An actually building for guards which holds as a kind of 'mini fort' holding a bed and a small supply of food, water and ammo has been suggested before and I whole heartedly approve. Bla-bla-bla.
You can already build beds and food stockpiles and ammo stockpiles. Why would you want a building with all of these, i.e. with nothing you can't do already?
Stockpiles getting priorities or special fill orders (if empty fill it NAO or smth like that) will probably be better, because of better application. No, it would actually be the best thing ever.